Iran's neighbors could play a decisive role in determining whether any sanctions aimed at curbing Tehran's nuclear ambitions are effective  and one Iran neighbor from whom the U.S. should expect little support on the issue is Pakistan. Ostensibly Washington's key ally in the troubled region, Pakistan also maintains a longtime (if sometimes fraught) friendship with Tehran. And as President Asif Ali Zardari's government moves to strengthen ties with its neighbor in a bid to enhance Pakistan's economic prospects, Islamabad is keen to sit out the nuclear dispute. While Pakistan insists that it is not actively encouraging Iran to join it in the élite club of nuclear-weapons states, officials in Islamabad appear decidedly untroubled by developments
across its southwestern border.

"The government of Pakistan, and the average Pakistani citizen, looks at
Iran as a friendly nation," Pakistan's Deputy Foreign Minister, Malik Amad Khan, told TIME in an interview. After Iran, Pakistan has the second largest Shi'ite Muslim population; its 33 million Shi'ites constitute nearly double the number in
Iraq. Before the 1979 Islamic revolution, both countries were members of the anti-Soviet CENTO security pact, and despite the Islamic Republic's aggressive
anti-U.S. stance, Pakistan became one of the first countries to recognize
Ayatullah Khomeini's regime. (See the top 10 players in Iran's power struggle.)

Pakistan's role in Iran's nuclear development has been more than passive spectator, however; Abdul Qadeer Khan, the father of Pakistan's atom bomb, admitted five years ago that he passed nuclear secrets to Tehran and Libya. The disclosures
stung Islamabad and forced then President Pervez Musharraf to act against Khan, before issuing a pardon and confining the proliferator, who is still hailed as a national hero in Pakistan, to house arrest. (See pictures of Pakistan's vulnerable North-West Frontier Province.)

Last month, A.Q. Khan briefly emerged from his hillside villa in Islamabad after the Lahore High Court lifted restraints on his movement. (Those restrictions have since been discreetly reimposed.) Unrepentant about his role in leading the world's largest proliferation network, Khan appeared in a rare television interview to cheer Iran's
nuclear program. "If Iran succeeds in acquiring nuclear technology, we will
be a strong bloc in the region to counter international pressure," Khan told the interviewer. "Iran's nuclear capability will neutralize Israel's power," he added, adopting the pan-Islamist rhetoric that has endeared him to conservative opinion in Pakistan.

Amad Khan, Pakistan's Deputy Foreign Minister, dismisses suggestions of
lingering Pakistani support for Iran's nuclear program. "We have a
three-tier system that prevents proliferation," he told TIME. But Islamabad
is happy for Tehran to acquire nuclear capability for energy uses. "Since
Iran is a signatory to the Non-Proliferation Treaty, if it requires
capability for energy, we have no problems with that." The Deputy Foreign
Minister added that Pakistan sees Iran as a "responsible" nation and
therefore "doesn't expect Iran to pursue nuclear-weapons capability." (Read "Rehabilitating Pakistan's Nuke Man?")

The Deputy Foreign Minister declined to comment on how Islamabad would react in the event of sanctions or tougher forms of pressure on Iran. Instead, Islamabad's focus remains on an "enhanced level of engagement" that can draw Iranian support for Pakistan's "energy, trade and communications" sectors. The new relationship with Iran has already seen a 28% rise in trade, according to Deputy Minister Khan, and with chronic shortages of electricity supply, Islamabad is eagerly awaiting the
construction of a decades-old proposed Iran-Pakistan gas pipeline  plans for
which remain doubtful.

Pakistan's weak civilian government also views Iranian influence as a potential foil to that of Saudi Arabia, which has stronger ties with the opposition. Government officials
privately accuse the Saudis of being prejudiced toward Zardari because of his Shi'ite background. (Shi'ites are an embattled minority in Saudi Arabia, whose dominant Wahabi strand of Islam deems them heretics.) But Pakistan's response to Iran will ultimately be determined by the all-powerful military establishment. And, analysts say, the army is a great deal more wary of Iran's regional aspirations. "They are not really allies," says Christine Fair of the RAND Corp. in Washington. "There is a misguided assumption that just because Pakistan gave Iran nuclear technology that they have some kind of strategic alliance." That deal, analysts say, arose out of former army chief General Mirza Aslam Beg's wish to "create problems for the
U.S." (See pictures of terrorism in Tehran.)

"Since then," says Fair, "Iran and Pakistan have been at loggerheads over a
range of issues." The Pakistani security establishment is wary of Tehran's relationship with India, and it suspects Iran of allowing its territory to be used by Indian-backed Baluch separatist fighters in southwestern Pakistan. Tehran, for its part, has repeatedly complained to Islamabad about cross-border attacks mounted by Jundullah, a shadowy Baluch militant group that uses Pakistani Baluchistan as a staging ground for attacks inside Iran. On May 28, the group claimed responsibility for a bombing that killed at
least 20 in the border town of Zahedan. Iran and Pakistan have also been at loggerheads over Afghanistan  Tehran has backed the Karzai government, and Pakistan is seen as continuing to covertly support the Taliban  and over the perception that Pakistan is not doing much to stem anti-Shi'ite sectarian terrorism by extremist groups on its own soil.

Even then, a number of different domestic political factors will keep Pakistan on the sidelines of any showdown over Iran's nuclear program. With anti-Americanism running high  an August poll by the Pew Research Center revealed that 64% of Pakistanis "regard [the U.S.] as an enemy"  backing new sanctions against Iran could provoke a domestic backlash. "It would be seen as
Pakistan against the Muslim world," says analyst Fair. (See pictures of people around the world protesting Iran's election.)

A related but deeper fear is that Iran has the means to make life exceedingly unpleasant for Pakistan should it side with Tehran's enemies. Already struggling with
a militant campaign that has ravaged the northwest and the tribal areas and
terrorized major cities, Pakistan, analysts say, can ill-afford a revival of
sectarian violence that plagued the country during the 1980s, when Saudi-backed Sunni militant groups clashed with Iranian-backed Shi'ite ones as part of a regional proxy war. Says Ayesha Siddiqa, an independent security analyst: "It isn't just
Iraq, Lebanon and Afghanistan where Iran can create trouble if it wants."